There are myriad types of cleaning compositions for cleaning textile fibers such as carpets, upholstery, drapery, clothing, bedding, linens, and the like. Most of these are based on soaps or detergents both of which are generically referred to as "surfactants". By "detergent" is meant a synthetic amphipathic molecule having a large non-polar hydrocarbon end that is oil-soluble and a polar end that is water soluble. Soap is also an amphipatic molecule made up an alkali salt, or mixture of salts, of long-chain fatty acids wherein the acid end is polar or hydrophilic and the fatty acid chain is non-polar or hydrophobic. Detergents are further classified as non-ionic, anionic or cationic. Anionic or nonionic detergents are the most common.
Surfactants, i.e. soaps and detergents, are formulated to loosen and disperse soil from textile fibers either physically or by chemical reaction. The soil can then be solubilized or suspended in such a manner that it can be removed from the fibers being cleaned. These function because the hydrophobic ends of the molecules coat or adhere to the surface of soils and oils and the water soluble hydrophilic (polar) ends are soluble in water and help to solubilize or disperse the soils and oils in an aqueous environment. The problems associated with the use of surfactants in cleaning fibers is that large amounts of water are generally required to remove the surfactants and suspended or dissolved particles. Also, surfactants generally leave an oily hydrophobic coating of the fiber surface. The inherent oily nature of the hydrophobic end of the surfactants causes premature resoiling even when the surfaces have a surfactant coating which is only a molecule thick. Surfactants also sometimes cause irritation or allergic reactions to people who are sensitive to these chemicals. There are also environmental problems associated with the use of soaps and detergents. Some are non-biodegradable and some contain excessive amounts of phosphates which are also environmentally undesirable. Up to now however, the inherent benefits of surfactants have out weighed the disadvantages of resoiling, skin, membrane or eye irritation, allergic reactions and environmental pollution.
This concern over health and the environment has prompted an emphasis on the use of less toxic more natural cleaning components. The quest for carpet cleaning compositions that have a balance of cleanability and resoiling resistance has resulted in compositions containing unnatural components that have a greater potential to cause allergenic reaction and other health and environmental problems. Normal soaps prepared from the base hydrolysis of naturally occurring fats and oils are not suitable for carpet cleaning because of the ability of their residues to attract soils. In order to make these residues less soil attracting, detergents are synthetically modified.
Oxidative yellowing or "brown out" as it is commonly called has long been a problem in carpet cleaning. The usual conditions that increase the potential for brown out are a higher pH cleaner and/or prolonged drying times Ordinarily the higher the concentration of solids in the cleaning composition the greater the potential for this oxidative yellowing to produce a noticeable discoloration on the carpet.
A significant improvement in the art of cleaning textile fibers, and carpets and upholstery in particular, is taught in U.S. Pat. No. 4,219,333. This patent shows that, when detergent solutions are carbonated and applied to the fibers, the solution rapidly penetrates the fibers and, through the effervescent action of the carbonation, quickly lifts the suspended soil and oil particles to the surface of the fiber from which they can be removed by vacuuming or transfer to an adsorptive surface such as to a rotating pad. Moreover, because less detergent solution needs to be applied to the fibers to effect the cleaning, the fibers dry more rapidly than do fibers treated with conventional steam cleaning or washing applications and little residue is left on the fibers. Although this process is clearly advantageous over prior art methods it still requires the use of some detergent and, in some instances, added phosphates, which are undesirable in today's environmentally conscious society.
In the past, in order to prepare a carbonated solution it was necessary to pressurize the cleaning solution in a container with carbon dioxide from an outside source, e.g. a CO.sub.2 cylinder, and shake the container, preferably during CO.sub.2 introduction, to insure that the solution was carbonated. Carbon dioxide tanks necessary to accomplish this pressurization are heavy and inconvenient to have on site for attachment to sprayers when cleaning solution is being applied to carpets. The benefits of carbon dioxide as a volatile builder salt have out weighed the inconvenience of having a carbon dioxide tank on location during cleaning. In addition, a disadvantage of externally carbonating a solution is that excess carbon dioxide may be expelled into the air or surrounding atmosphere and there is always the danger that carbon dioxide can be expelled accidentally from the pressurized cylinder in which it is contained.
Commercial synthetic detergents also have a tendency to foam. This foaming has been found to interfere with cleaning even in carbonated solutions since the absorbent pad, as referred to above, is caused to glide over the foam rather than contact the carpet fibers. Normally additional synthetic antifoaming agents are added to cleaning solutions to prevent foaming. These antifoaming agents are normally oily and can decrease resoiling resistance.
Urea has been added to synthetic detergent compositions which contain as the active ingredients monoalkyl ethers of polyoxyalkylene glycols, monoalkyl ether of polyethylene glycol, glycerine and/or propylene glycol, disodium edetate (Soviet Union Patent 1618758, Jan. 7, 1991). Urea is an optional additive to a low temperature detergent containing nonionic or anionic surfactants and a host of other ingredients such as solvents, enzymes and the like. See for example the following German Democratic Republic Patents GDR Patents 286178, 286179, 286180, and 286181, all dated Jan. 17, 1991. German Republic Patent 4001688, Aug. 16, 1990, discloses a creamy powder containing an adsorptive organic or inorganic powder mixture, water and antistatics with 1-10% weight of urea or urea derivatives, and/or cyclic carboxamides dissolved in water. None of the above references disclose non-detergent cleaning compositions containing the combination of carbon dioxide and urea as being the active cleaning ingredients in an aqueous solution.